Beacon-based networks are based on beacon technologies, and are a type of single-hop or multi-hop ad hoc network formed through beacon synchronization. Currently, many types of networks such as radio sensor networks are based on beacon technologies.
Nodes in a beacon-based network are classified into a coordinator node and a device node. The coordinator node is responsible for coordinating communication and sending necessary network information. The device node joins the network by monitoring network information sent by the coordinator node, and communicate with another node as coordinated by the coordinator node. A node that already joins the network may serve as both a coordinator node and a device node. When this node coordinates communication of another node and sends necessary network information, this node serves as a coordinator node; when this node accepts coordination performed by another coordinator node and communicates with another node, this node serves as a device node.
The process of a device node joining a network is also known as an association process. The association may be association arising from the device node joining the network initially, or may be reassociation caused by the mobility of the device node.
A general association process is: A pending node monitors beacons (also known as beacon frames), each of which specifies the communication time sequence of nodes (such as a dedicated communication timeslot allocated to the node) and network information (such as the period of a beacon and duration of a superframe). The pending node sends an association request to a target coordinator node according to a beacon when the beacon is monitored. The coordinator node receives the association request, and returns an association response to the pending node if approving the pending node to join the network. The pending node is associated after receiving the association response.
Generally, the beacon is sent periodically, and the sending period is D×2BO, where BO (Beacon Order, Beacon Order) is a parameter which decides the communication time sequence of nodes, and D is basic superframe duration. If merely one coordinator node exists in a radio sensor network and no receiving error occurs, the pending node monitors a beacon at a mean interval of ½×D×2BO. The mean interval affects association delay. At a 2.4 GHz band, delay (D)=15.36 ms. If BO=10, the mean interval is 7.86 s, namely, the mean association delay is at least 7.86 s. Besides, the channel environment in an actual network is not as good as expected, and collisions generally exist in the network. Consequently, the pending node does not receive every beacon successfully, and the association delay is even larger.